For those who stumble upon this: this can be caused e.g. by trying Toolbox, realizing it's annoying junk and uninstalling — you'll get stuck with no updates and this message then. The fix is to remove `-Dide.no.platform.update=true` from `pycharm.vmoptions' file (on Macs, this is located in ~/Library/Preferences/PyCharm20??.?).